Did the RAF have designs for a long range escort fighter?

[Shortround6]

So this brings me to the next question, if Leigh-Mallory's team assessed a Spitfire IX with a 45gal external tank had an operational range of 230 miles, how was it that the Mustang with only 30 extra gallons more fuel than the Spitfire and NO drop tanks was, according to Shortround6, rated by the USAAF to fly 460 miles?

The answer, I believe, is in the willingness of the respective RAF and USAAF communities to accept the operational risk. If every worst-case argument defines the figures the commander chooses not to accept the risk. This is what I think Leigh-Mallory did. Whereas the USN fighters in the Pacific (flying up to 600 miles – mostly over the sea ref: Gregory Boyington, Baa Baa Black Sheep, London, Putnam, 1958, p. 147-148) and those of the USAAF, led by Kepner had a totally different perspective; they was much more aggressive and, therefore, willing to take the operational risk.

For instance the Americans learned not to drop their drop tanks at the first sight of other aircraft, as the Germans had realised the P-47 vulnerability in this regard quite early.

Indeed, AIR/556 FC/S.29970/Ops.1 dated 28 Dec 1944 recognised this noting that 'navigation by fighters, once they are airborne is purely D.R. 'and that such dead reckoning 'navigation is very satisfactory and is uniformly better than the bombers''. Indeed, it was 'so good that unless the weather is appalling, little use is made of the homing facilities, which are first class.

'Drop tanks are never dropped unless positive identification of the Hun has been made.'

'Training consists almost entirely of instrument flying and formation, at which they are much better than we are. The weather makes little difference except for landing and they will land in much worse conditions than we will. It should be noted that the fighters will take off, land and operate in worse weather than the bombers without any blind approach facilities. No gunnery training, no night flying and practically no cross-country training are undertaken.' Finally in the Conclusions the report assessed the Americans as 'much more go ahead than we are' and 'much greater realists'.

The Americans asked 'if there is any real need for night flying training for the amount of night flying' they did. 'If they are going to crash at night in operational aircraft why not let them do it operationally, why practice.' and "I know its no fun to fly with the fuselage tank full but if we can lets do it, in any case no war is fun and we gain operationally'

So the difference, in my opinion comes down to leadership and risk management; something the Americans handled better than the British.

I believe you read the sentence wrong. It may be my fault for the way I arranged it.

"USAAF rated the Mustang at a 150 mile radius with that much fuel and NO drop tanks and 460 miles (?) with about 120/125 IMP gallons worth of drop tanks.

The 460 miles had very little to do with "operational risk". It had a lot to do with having 120-150imp gallons left in the inside tanks at the start of a fight.

Navy ranges in the Pacific are rather useless comparisons because slower cruise speeds (more economical) and lower altitudes could be used as there were rarely extra enemy bases between the attackers base and the defenders base. It can take several minutes to go from around 200mph to close to max speed in level flight and if enemy fighters attack from above they are attacking at higher than level speed. The British and Americans found that in areas that were likely to have enemy fighters the allied fighters should keep their speeds over 300mph and this cut into the range. Granted many times the fighters that escorted on the way in were relieved by fresh squadrons on the way back and no longer had to weave to keep station with the slower bombers (burning more fuel) and could fly relatively straight courses home, dodging known flak concentrations and known fighter fields.

Losing planes (and pilots) that have to come from factories 3-5000 miles away (for the US) due to running out of gas (poor planning) is not "risk management". The Americans did do a pretty good job of it, but that report fails to take into account several things or at least to put them into proper perspective. Like 'If they are going to crash at night in operational aircraft why not let them do it operationally, why practice.' Again those "operational aircraft" had to be brought from the US aboard ships. It may also ignore the amount of training the US pilots got in the US before being sent overseas. Many US pilots got 10-20 hours on Planes like P-40s before being sent to combat squadrons, some got at least a few hours on P-47s and P-51s states side before going overseas. Any fuel for training flights has to be brought from the US. US pilots did cross country training in the US.

as a further view on the Spitfire as a long range escort compare it to a P-47. The P-47 was perfectly capable of flying over 800 miles on internal fuel at economical cruising speeds (no reserve but take-allowance). The trouble with the combat radius came in with huge increase in fuel consumption at combat or near combat powers. Book or yard stick ranges sometimes bare little resemblance to Yardstick ranges.
The British might have been able to turn the Spitfire into a long range escort but not an effective one (or available in numbers ) until very late 1942 or early 1943, ( MK VIII went operational in June of 1943)

 

[tomo pauk]

perhaps: lets look at two data sheets (if any one has a better one for the spitfire please post)
http://www.spitfireperformance.com/spit8adsaussie.jpg
http://www.wwiiaircraftperformance.org/mustang/mustang-III-ads-3.jpg

Please note that the Mustang, with it's extra 30 gal of fuel is good for a "nominal" extra 210 miles range at economical speed ( which is 33mph faster than the Spitfire). USAAF rated the Mustang at a 150 mile radius with that much fuel and NO drop tanks and 460 miles (?) with about 120/125 IMP gallons worth of drop tanks. Data sheet says the Mustang is good for 1710 miles of "range" with that fuel load. the MK VIII is good for a 'nominal' 1265 miles with a 90 gallon drop tank. Granted if escorting British bombers the escorts won't have to cruise quite so high and less fuel is burned getting to altitude and perhaps cruise is a bit better (?).
See this page for difference in climb for a MK IX with and without a 30 gallon exterior tank.
http://www.spitfireperformance.com/bf274climb.jpg

If you can afford the performance "hit" so be it. 30 gals of fuel is closer to 300lbs of weight including tankage.

Thanks for the listed data.
The 2-stage Spitfires were much better climbers than the Fw-190s (main threat in the West from early 1942 on), and at least as good as Bf-109F4/G1/G2, especially above 20000 ft, so the extra 30 gal tank will not be that much of a harm to the actual performance difference. 2-stage Spitfire also climbs better than the US long rangers (P-51, -47, -38). For mid 1943, the better Merlins are available (63, 66, 70 series) than the Mk.61; Spit VIII never used the Merlin 61?
The Spitfire Mk.VIII, with extra 50 gals in rear fuselage tank, would be the best most useful Allied fighter in 1943, had that extra tank was installed. And cheap, as icing on the cake.

Yes and no. It may help negate the threat to the bombers somewhat but it means the Fighters, even if operated in relays and not tied to the bombers from beginning to end have to maintain a high cruising speed ( 50%-100% higher fuel consumption per hour) to help avoid being bounced themselves, both in going and out going. You have to keep the rate of attrition low for BOTH the bombers and fighters.

With all the Spitfires having a bit greater internal fuel tankage, the Germans in the ETO will have to withstand both them and bombers' defensive fire. Since the LW would not be able to concentrate the fighters located in different occupied countries in the West, plus different parts of Germany, the RAF would have enjoyed the numerical superiority, 2:1 or better? That beats the 5% difference in RoC handily. Plus we have the bombers defensive fire to the RAF's advantage.

American system shows up too late to do any real good.

Unlike the British

Plus the weight of the tank/s. and 20 more gallons is only 104 gallons? 20 gallons won't run the engine for more than 30 minutes even at moderate cruise speeds(if that, about 17 minutes at max cruise or about 100 miles at max cruise at 20,000ft). It requires very careful juggling of cruise speeds to gain any real benefit from 20 gals unless the goal is to bomb further into the low countries and leave Germany untouched.

On the return leg, the fighter can cruise at 300 mph, the extra 20 gals means there is enough fuel to make it from Continental coast (Belgium, Neth.) to the base.

 

[tomo pauk]

This already is a circular argument and it is driving me nuts. This is a thread entitled "Did the RAF have any designs for a long range fighter escort"? I asked the simple question "what would an RAF long range escort, escort" To my mind no RAF bomber was ever capable of it in daylight except the mosquito. They didn't have the defense or the altitude performance. However I have been convinced by the technical arguments. 0.303mm brownings mounted in turrets were ample to defend a formation and so there was no reason for the RAF shouldn't mount daylight raids with their Stirlings, Halifaxes and Lancasters as and when available, it must be a mystery why they didn't. Additionally there was no reason for a long range escort for the US daylight bombers. I presume the US was just too full of aluminium merlins and pilots.

In answer to the thread question, long range escorts were never necessary so the RAF didn't bother.
Source: This thread

We can recall that British were fighting in the MTO from mid 1940 on, and in SE Asia from late 1941. There the long range was essential, hence a very attractive feature an aircraft could posses. The LR escort will escort whatever Allied bomber needed escorting. The situation in MTO even meant that USAF pressed the A-36 (yes, the dive bombers) to escort their B-25s. Long range fighter would be able to provide defense for the Malta convoys, and put further pressure on Italian and LW assets once the invasion of Sicily and Italy is planed and beyond.
The RAF was also involved in prolonged struggle vs. LW in the ETO from early 1941 on, and more range was one of the things desired. Especially once the better LW fighters emerged, and the pilots being advised to cruise fast (so they don't get easily bounced), rather than slow, that burned more fuel than slow cruise.

 

[stona]

Don't want too much of a diversion, but weren't Beaufighters used to protect the Malta convoys?

Cheers

Steve

 

[tomo pauk]

I've asked that question some time ago, but the never get the worthwhile answer. I'd appreciate it if someone has some good data on this.

 

[stubbsy]

"In answer to the thread question, long range escorts were never necessary so the RAF didn't bother.
Source: This thread

Well, Churchill, when he wrote to Portal on 7 Oct 1941, suggested that the RAF ought to provision LR fighters to denude enemy AD and enable a daylight bombing campaign to resume. Portal's reassurance that fighter protection would be required implicitly acknowledged the limitations of not provisioning a LR fighter.

Moreover, Donald Stephenson, AOC No2 Bomber Group, in Sep 1941 wrote to Pierce, AO C-in-C Bomber Command, and Slessor AOC No 5 Bomber Group seeking 'Fighter Command, or someone else gets busy and thinks out the right kind of equipment and tactics to carry the bomber offensive safely through an enemy air defence system in daylight.

So a requirement was articulated from the very top and by someone at the operational level, only it didn't get past the Portal/Sholto Douglas/Leigh-Mallory strategic/operational divide.

 

[Shortround6]

Don't want too much of a diversion, but weren't Beaufighters used to protect the Malta convoys?

I've asked that question some time ago, but the never get the worthwhile answer. I'd appreciate it if someone has some good data on this.

This may depend on what is meant by "escort" pr "protect" as Beaufighters could certainly cause a lot of problems for Italian or German bombers trying to hit the convoys but then the Axis bombers could very well be operating beyond the range of axis single engine fighters or at the edge of the single engine fighters effective range.
A bit like the Fulmars doing a good job of Fleet/convoy defense when put up against SM 79s and such. Not so good a job if they faced Single engine fighters escorting the bombers.

 

[Glider]

Don't want too much of a diversion, but weren't Beaufighters used to protect the Malta convoys?

Cheers

Steve

Yes, but only because there was nothing else and the importance of the convoys were paramount. They modified the Spitfire V to carry 2 x 45gallon drop tanks and installed a 20mm in the nose of the Blenheim IVf, almost anything to help the convoys.

 

[stubbsy]

So to sum up where I am coming from; Did the RAF have designs for a long range escort fighter?

1. Not really, because Portal, Sholto Douglas and Leigh-Mallory were convinced the Spitfire, modified with LR tanks, couldn't compete with its LW adversaries.

2. But, a strategic requirement had been set by Churchill (see above) and supported by Stevenson (see above).

3. The only aircraft the RAF had that was available in sufficient numbers and could fulfil this requirement, in terms of dog-fighting/air-to-air combat, was the Spitfire.

4. Extra internal fuel could have been incorporated into the Spitfire design; to the rear of the cockpit and in the wing leading edges, providing an extra 40/72 and 32 gals respectively. The RAF was lethargic in defining this requirement as a priority because of 1 above.

5. What would the Spitfire's operational range have been with these modifications. This is where the experts on this forum would be a great help, to come up with an agreed number in n/miles.

6. So What? Well, if my rough - finger in the air - assessment of the figures is right the bombers could have been escorted to ranges which means they didn't have to bomb France, maybe into Germany.

7. So What? Well, the point raised above that the RAF didn't have sufficient fighters to do the escorting and make an effective contribution is worthy of discussion. But what if they were ready to do so when the American LR fighters came on line in mid to late 1943 - and the Americans hadn't been diverted by the idea of the YB-40, an idea that chimed a little too closely with Sholto Douglas's view on self-protecting bombers. POINTBLANK's objectives could have been achieved earlier, with greater RAF support, and precision daylight bombing by the RAF and USAAF could have taken place before they were required to support OVERLORD. Certainly, the LW had downsized in the West after Barbarossa and would have needed to reconfigure to try and stop the bombing. This would have eased the pressure on the Russian front, helping our allies.

8. What about external fuel for the Spitfire; either the 45 gallon or the 2 x 62 gallon tanks? These would have made a significant difference to the range of the Spitfire and although the figures for what was needed to return to the UK - in posts above from other contributors - would limit the operational range of aircraft so equipped, the effectiveness of the joint counter-air campaign would have defined the parameters for the operation risk/benefit equation, requiring a leadership decision on what risks to take. As the Fighter Command Ops 1a officer commented, above, the Americans were less averse to the risk, which was tough on their pilots admittedly, but war is war, and tough decisions had to be made. Kepner certainly made them wrt LR fighters, Leigh-Mallory didn't.

Thoughts?

 

[stubbsy]

A good question on what escort and protect meant. The minutes of the Air Fighting Sub Committee discussed this issue in 1937, see below:

 

[tomo pauk]

....

8. What about external fuel for the Spitfire; either the 45 gallon or the 2 x 62 gallon tanks? These would have made a significant difference to the range of the Spitfire and although the figures for what was needed to return to the UK - in posts above from other contributors - would limit the operational range of aircraft so equipped, the effectiveness of the joint counter-air campaign would have defined the parameters for the operation risk/benefit equation, requiring a leadership decision on what risks to take. As the Fighter Command Ops 1a officer commented, above, the Americans were less averse to the risk, which was tough on their pilots admittedly, but war is war, and tough decisions had to be made. Kepner certainly made them wrt LR fighters, Leigh-Mallory didn't.

The Spitfire have had a variety of drop tanks, most notably the one with 90 imp gals, along with 170 imp gals size. Those are mounted under fuselage.
The 62 imp gals are the US produced tanks - 75 US gals. Two were installed under wings, on the US modified Spitfire IX. Need also new plumbing, and it will impose some drag/speed penalty, like it was the case in P-51A/B/C (12 mph cost was there, due to the wing racks). So I'd stick with historical British gear for the drop tanks facility.

The US modified Spit, along with other variations to the theme: link.

 

[Mike Williams]

I have to admit, I'm not seeing the point of all the debate. That said, this is what comes to mind regarding RAF fighters and and long range day escort.

65 Squadron was first RAF unit to convert to Mustang III, this occuring in December 1943 - around the same time as the 354th and 357th Fighter Groups (9th AF at the time) first went operational with the P-51B.
RAF units to use the Merlin Mustang in the ETO and MTO were 65, 122, 19, 306, 315, 129, 316, 541, 234, 309, 64, 126, 165, 118, 611, 303, 112, 213, 249, 260; RCAF:- 441, 442.

Here's an example of RAF Mustangs operating with 8th AAF Mustangs escorting 8th AF bombers.
http://www.wwiiaircraftperformance.org/fo-312-map.jpg

For example, here' a combat report that I have handy showing Mustang IIIs escorting Lancasters to Germany.
http://www.wwiiaircraftperformance.org/mustang/combat-reports/129-davis-23march45.jpg

There were 1006 Mustang III and IVs on strength with the RAF as of 26 April 1945.
http://www.spitfireperformance.com/RAF_Strength_26april1945.pdf

I happened to have these on hand, but these documents show that Spitfire XIV were escorting Lancasters and Halifaxs to Germany by day as of September 1944. I'm sure other documents are available showing earlier day escorts of RAF heavy bombers by other units.
http://www.wwiiaircraftperformance.org/350-ORB-11Sept44.jpg
http://www.wwiiaircraftperformance.org/130_Oprep-12Sept44.jpg
http://www.wwiiaircraftperformance.org/402-Form541-12Sept44.jpg
http://www.wwiiaircraftperformance.org/610-ORB-1sept44.jpg

 

[Glider]

I do like reading these original documents, you pick up things that you don't expect. I notice on the last paper on the 3rd September they reinstalled the 303 guns. It looks as if they were taken off for the anti diver missions. A little something I didn't anticipate

 

[stubbsy]

I have to admit, I'm not seeing the point of all the debate. That said, this is what comes to mind regarding RAF fighters and and long range day escort.


I happened to have these on hand, but these documents show that Spitfire XIV were escorting Lancasters and Halifaxs to Germany by day as of September 1944. I'm sure other documents are available showing earlier day escorts of RAF heavy bombers by other units.

http://www.wwiiaircraftperformance.org/610-ORB-1sept44.jpg

Mike,

From my perspective the point of the debate surrounds a issues of ethics and morality and a number of counterfactuals or what if's.

Firstly, the RAF bombed by night to avoid German fighters because when in bombed by day, as they had planned before the war, without fighter escorts the RAF had deemed it didn't need, it suffered unacceptable losses. Moreover, until 1943 when night bombing technology improved sufficiently it bombed (generally) inaccurately and Bomber Command, despite Harris latching on to any and all elements of positive INT reports on the accuracy and damage caused by bombing, while simultaneously choosing to ignore or disparage the detractors. So, in my opinion, by choosing not to have LR fighter escorts from 1937 onwards, until Sep 1944, the RAF implicitly accepted the inaccuracies of its night bombing campaign, along with the civilian casualties caused as a necessary method of waging war. Richard Overy covers the ground excellently in his 2013 book 'The Bomber War'.

Secondly, by doing nothing to create LR fighters from 1939 to 1943 the RAF chose to continue with a night bombing campaign. Discussion may centre on what exactly LR means. For me, in WW2, this meant having an operational range of around 400 miles. In this context the operational range of the Mustang III reached that target in 1944, but even the later model Spitfire's stuggled to reach this target.

Thirdly, the RAF didn't see its fighter role in supporting POINTBLANK to any great degree, instead they deferred to the USAAF to achieve its aims. But, if the RAF had a LR fighter, POINTBLANK could have been concluded earlier and RAF and USAAF bomber and fighter raids could have been coordinated, by day, concurrently, against strategic targets with precision in late 1943 or very early in 1944. Attacking Oil with precision, as Harris later acknowledged though he still considered oil to be an 'outsider' target, could have been decisive and stopped the German land fighting machine as it did in 1945. Finishing the war almost a year earlier would have saved a lot of lives.

Fouthly, the issue of 90 gallon slipper tanks and the RAF taking part in daylight escort missions from September 1944 is very interesting. Why? Because on 5 September the RAF stopped the trials at Boscombe Down on the USAF modified Spitfires (though they resumed later - see earlier post for such trials in 1945)w hich had achieved cruise ranges of 1240 and 1365 miles. I think the embarrassment the USAAF caused resulted in the decision to start a larger programme to escort RAF bombers over Germany. It is therefore coincident that the Spitfire of 610 Sqn flew such mission of 6 September, albeit to a target to the West of Germany, using a 90 gallon slipper tank. When resupplying Malta it had been deemed too dangerous to allow the Spitfires to fly armed with 90 gallon slipper tanks as it was thought the aircraft would be at a disadvantage against LW short-range fighters, so they were advised to avoid, rather than engage, the LW. See Geoffrey Wellum, First Light. So, why the change in Sep 1944? Quite simply, the risk had diminished because the USAAF had largely destroyed the fighting power of the LW from Jan to April 1944 in POINTBLANK. I see the report showed no contact made with the LW in the sqns maiden trip to Germany.

Hope this synopsis helps the case for the discussion?

 

[drgondog]

By definition (for me), the discussion of Long Range Fighter should be coupled with planned maximum Combat Radius.

The discussions surrounding external tanks is relevant to the extent that the long range tanks will get that fighter, in escort role, to its maximum distance and a.) drop them, b.) engage in combat solely on internal fuel, and c.) return in a straight line back to base with a reserve amount sufficient for at least 30 minutes in case of bad weather or other delays.

Thus - any discussion regarding a Spitfire VII or P-47D-11 or P-51B-1 or P-38J-5 in the context of Combat Radius looks to the maximum practical reserve of internal fuel remaining after start, warm up, taxi, assemble before switching to external fuel tanks. From a planning standpoint that is all the remains to fight for 20 minutes and return home at the farthest practical escort distance.

Before the P-51B obtained field modification 85 gallon tank, or the P-38J-15 arrived with extra leading edge 110 gallons, or P-47D-25 arrived with extra 60 gallons of internal fuel, even these 'long range escorts' had not achieved their potential.

I find it curious that RAF withheld Spitfires equipped with 'Slipper Tanks' from daylight escort based on some notion that they 'might be attacked' by coastal LW units - US fighters always confronted that possibility and shrugged it off... if it happened, they dropped tanks, engaged and made an assessment regarding how much further they could go - and returned then while the unmolested escorts continued as planned.

 

[Mike Williams]

Fouthly, the issue of 90 gallon slipper tanks and the RAF taking part in daylight escort missions from September 1944 is very interesting. Why? Because on 5 September the RAF stopped the trials at Boscombe Down on the USAF modified Spitfires (though they resumed later - see earlier post for such trials in 1945)w hich had achieved cruise ranges of 1240 and 1365 miles.

stubbsy, I wouldn't get hung up on that 610 Squadron mention of 90 gallons tanks in September. Other Spitfire XIV units were already using 90 gallon drop tanks in the spring of 1944, see for example:

91 Squadron Diary, 11 May 1944

322 Squadron Operations Record Book, 19 May 1944

If memory serves, Spitfire VIIIs and IXs were using them earlier than that.

 

[stona]

As of 1942, and Harris' arrival, it is true to say that Bomber Command chose the night time option. Harris rejected any attempts to divert him from his campaign. Before then I don't think it was a choice. It was forced on Bomber Command and nobody seems really to have worked out what to do. The Command was anyway in denial about the abysmal results it was actually achieving. In all the eventual agonising about the inaccuracies of night time bombing the possibility of returning to a day time campaign is rarely mentioned (I can't actually think of a single instance) in 1941/42/, nor therefore is the possibility of fighter escorted missions, excluding of course the aptly named 'Circus' operations which served, badly, an entirely different purpose. Unescorted daylight missions by specially adapted bombers were briefly on the agenda
Cheers
Steve

 

[tomo pauk]

...

If memory serves, Spitfire VIIIs and IXs were using them earlier than that.

And Spitfire Vs even earlier.

 

[Edgar Brooks]

From my perspective the point of the debate surrounds a issues of ethics and morality and a number of counterfactuals or what if's.
Hope this synopsis helps the case for the discussion?

Unfortunately you make too many assumptions:-
First, the RAF didn't "implicitly accept" anything, tactics were dictated by the Air Ministry, and the RAF did as it was told. Bombing aids H2S, Oboe, Gee-H were in use long before September 1944, in fact they were offered to the USAAF in September 1943. Also the civilian casualties were a deliberate policy, introduced in September 1941 to destroy morale (didn't work, of course.)
Second (really an extension of the first) the RAF did not choose to continue the bombing campaign, neither did they choose to do without a long-range fighter. As always, they did as they were told; nobody ever explains how you escort individual aircraft (bombers never flew in Groups, never mind Squadrons,) when every gunner is itching to open fire on twin, or single, engine fighter he sees one, or the pilot, acting on a sighting report, corkscrews down, and out of sight.
Third, you really should check on how often Spitfires were sent out to cover the return of USAAF bombers, after they'd had their original escort drawn away, and suffered a mauling.
Fourth, trials on the U.S.-modified Spitfires were halted because the "work" done on the wings had, in the Air Ministry's view, weakened the structure enough to make the aircraft not combat-worthy. The U.K. worked with flexible tanks, aka "Mareng bags," which enabled the wings to retain their integrity.
Aircraft, heading for Malta, were not told to avoid combat due to fear of the danger, but because the authorities wanted them to hang on to the ferry tanks, and preferably land with them intact, since there was a shortage, and they could be returned to Gibraltar for future re-use.

 

[pbehn]

The strange thing about this thread and the question it poses is that I don't think any country designed a long range escort. The P51 Mustang was such a beautiful plane and so fantastic at the job of escorting bombers that it is difficult to believe it wasn't designed for the job. The P51 was commissioned by the British purely to be a fighter better than the P40. It is a pure and happy coincidence that the original Allison engine could be replaced by a merlin, and that the merlin could be boosted to massively increase its original 850BHP and its impressive internal fuel load could be increased internally and externally and . and.... and ....and it is a long story.
The P47 was designed as an interceptor but in its N version was a very good long range escort.

The role of long range escort sprang up quickly and was solved very quickly. The British started bombing at night and the US was convinced until proved otherwise that bombers could protect themselves. The British could have stretched the Spitfire in the same way the Corsair was having a larger main tank in a longer fuselage or perhaps rearranged the wing. The Spitfires wing had leading edge tanks which were conversions of the evaporated cooling system abandoned long before the war started. The bays were still pretty much still as originally laid out, why not a re design with 2 x 0.5in mgs in the outer part of the wing and the inner part for extra fuel, with an extra tank behind the pilot and drop tanks, it could be useful. The Mustang would always hold the upper hand because of its low drag. However for much of the war the British were occupied with getting the better of the FW190 and later Bf109s, putting bigger tanks inside a bigger fuselage wouldn't do that.